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In the eyes of the CIO, desktop virtualization dramatically reduces support costs, improves security and streamlines application deployment.

On the networking side of the house, the benefits can seemed clouded by a plethora of challenges resulting from the need to optimize application performance using existing bandwidth.

Regardless of the apparent hassle, the network team must firm up strategies to prioritize traffic, manage bandwidth and ensure application performance to these virtual desktops. And the needs can change depending on the type of client used and whether virtual desktop infrastructure (VDI) is server- or desktop-centric.

Understanding desktop virtualization clients

Desktop virtualization can involve a host of different clients -- all of which have different bandwidth and support needs:

Thick client -- Thick clients are standard desktops or laptop PCs that use an operating system in addition to running a virtual image or terminal services. In a typical scenario, the users are part of the help-desk function for a period of the day, during which time they run a separate virtual desktop image or just terminal services. The downside of this option is that IT still has to service full desktops that require regular updates, patches and support. Many companies use thick clients to pilot desktop virtualization.

Net client -- Net clients are in between thick and thin clients. They run stripped down OSs or can be mobile devices like the iPhone running Citrix receiver for iPhone or Wyse's Apple iPhone App.

Zero client -- With a zero client, all of the OS or applications run on the server with nothing at the desktop. The zero client is essentially an extension cord that extends the keyboard, mouse, screen, audio, printer and USB ports to the desktop. This solution works best in hazardous environments and environments where maintenance is a challenge. Zero-client desktops are excellent for factory floors, chemical plants and hospitals. Zero clients also draw much less power than a conventional desktop or even a thin client.

Bandwidth requirements vary by protocol, architecture, application and client. For server-centric desktop virtualization, the main issue is delivery of graphics and real-time applications. For desktop-centric virtualization, the issues are the delivery of a whole operating image quickly enough at the start of a session, and potentially re-syncing to a central distribution system at the end. This not only puts significant demands on the network, it also puts demands on storage.

Graphics and real-time communications are the greatest network issues for server-centric desktop virtualization. At the low end of the spectrum, a basic terminal services session with Remote Desktop Protocol (RDP) requires 56 Kbit/s-100 Kbit/s. A higher bandwidth option is PC over IP (PCoIP). PCoIP (developed by Teradici and the core protocol of VMware View) can easily chew up 100 Mbit/s on the LAN with WAN throughput as low as 1 Mbit/s. In fact, VMware has demonstrated View with good performance at speeds as low as 125 Kbit/s with latency as high as 250 msec.

There are a number of techniques to optimize graphics in a VDI. These include:

Video rendering on client and server: Intelligently display video by matching resolution to actual bandwidth available

Distributed caching to support multiple clients using the same data: strategic location of data as close to the client as possible to minimize WAN bandwidth requirements.

Real-time communication is particularly sensitive to three issues: packet loss, latency and jitter. Management requires intelligence at both ends of the connection, something lacking on thin- and zero-client solutions. Therefore, vendors need to go to great lengths to perform bandwidth management from the server end of the connection.

To address these challenges, the network administrator should look for the following features to optimize network resources for real-time communications:

Compression of streaming data -- Use standard data compression techniques to lower the number of bits transported, thus providing the same performance at lower bit rates.

Artificial fragmentation of other traffic to ensure minimal latencies -- Create a more consistent packet size by fragmenting large block-size data to reduce jitter and latency for real-time and desktop virtualization protocols.

Desktop virtualization and unified communications: Not a love story

Providing continuous, real-time communications requires strong network and performance management -- simply adding bandwidth is not enough. In particular, an emerging challenge is the intersection of unified communications (UC) and desktop virtualization. Less than 5% of organizations currently integrate their UC efforts with desktop virtualization. They find that most desktop UC clients won't support voice and video in a desktop virtualization environment.

Enterprises that are UC dependent must pilot any desktop virtualization application before committing to rollout. In the meantime, Citrix appears to be in the lead in optimizing for UC with its HDX High Definition User technology. Competitors are bound to follow shortly.

Storage storms ahead

As discussed, extraction of the user experience from the underlying OS and application puts significant demands on the network, depending on the type of virtualization, client and application. Similarly, extracting storage from the end user puts significant demands on the network. In this article the emphasis has been on how the network affects the user in a VDI environment. In the next article, we will look at how storage affects network infrastructure in VDI.

About the author:Ted Ritter is a senior research analyst with Nemertes Research, where he conducts research, advises clients, and delivers strategic seminars. A Certified Information Systems Security Professional (CISSP), Mr. Ritter leads Nemertes' research on information stewardship, which includes compliance, as well as the management, access, storage and back up of data.

Mr. Ritter has designed, implemented and supported telecom and information security solutions for commercial, federal and international clients. He holds a master's degree in telecommunications management from The George Washington University and a bachelor's degree in neuroscience from Oberlin College.

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